Switch tube device for waveguides



. June 9, 1959 R. A. HAGAN v 2,890 419 I SWITCH TUBE DEVICE FOR WAVEGUIDES Filed March 30, 1955 Fig. I

Q ;--3? 37- fl 39 27 242 39 g Llo O i |o I6) I 1 l |9- "H' lag INVENTOR. RICHARD A. HA GAN ATTORNEY Unite States Patent SWITCH TUBE DEVICE FOR WAVEGUIDES Richard A. Hagan, Reading, Mass, assignor, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Application March 30, 1955, Serial No. 497,888

4 2 Claims. ('Cl. 333-13) This invention relates to gaseous electronic devices and more particularly to switching devices employed for controlling the transmission of high frequency electromagnetic energy in waveguides.

The novel features of this invention are particularly useful in electronic tubes of the A-T-R (anti-transmit-receive) type such as those employed in radar systems for preventing return of substantial portions of the echo signal energy to the source of the broadcast energy. However, it will be obvious from the following description that some or all of these features may be useful in devices of other types.

A-TR tubes of the type heretofore employed generally include a resonant cavity filled with an ioniz able gas in which a discharge flashes when the tube is subjected to a high level burst of electromagnetic energy. A window is provided in one extremity of the cavity for admission of high frequency energy to the cavity from the waveguide with which the tube is associated. Commonly, the window includes an electrically conductive frame portion defining a central aperture sealed by a suitable dielectric material to prevent escape of the gas-fill of the tube. Heretofore, in order to mount these tubes on the waveguide it has been necessary to provide an opening in the wall of the waveguide to receive the window of the tube and also a mount for holding the tube in proper position with respect to the opening.

The positioning of the tube so that the window is flush with the inner surface of the waveguide is of extreme importance to the proper functioning of the tube and the associated components of the system. In one type of prior art mounting arrangement, the problem of achieving proper contact between the window and the waveguide is avoided to some extent by deliberately spacing the window from the edges of the opening in the waveguide. This is accomplished by providing a box-like arrangement or choke-mount around the opening in the waveguide which is adapted to receive and support the tube in proper position. The box is sufficiently larger than the tube to afford an annular space, usually one wavelength long, between the outer surface of the tube and the inner surface of the box thus establishing a choke coupling of the tube and mount with the waveguide. This results in an extremely bulky assembly which complicates many applications, particularly where transmission of energy at shorter wavelengths, or broadband operation is involved, or where it is necessary or desirable to employ a plurality of AT-R tubes and/ or a T-R tube in close proximity. In addition, arcing tends to occur at the gap between the exterior of the tube and the inside of the mount during transmission of energy at high level in the waveguide. Still further, some systems can set up higher order modes in the choke mount which result in undesirable performance characteristics.

In the known, so-called direct-contact type tubes, no choke coupling of the tube to the waveguide is employed. Instead, the edge of the Window may be beveled and the edge of the opening in the waveguide correspondingly beveled to provide a seat for the window of the tube. This demands machining of the beveled surfaces to very close tolerances to achieve proper location of the window exactly flush with the inner surface of the waveguide. In still another direct contact type tube beveled surfaces as described above are avoided by providing a shoulder on the tube a short distance back from the window and the tube is inserted in the opening in the waveguide with a metal gasket between the shoulder and the outer surface of the waveguide to achieve the necessary electrical contact between tube and Waveguide. Either of these direct contact type arrangements necessarily include bulky and accurately machined clamping and mounting arrangements for holding the tubes in position. Furthermore, despite extreme care in fabrication of tubes and mounts and in the adjustment of the position of the tubes with respect to the waveguides, unavoidable discontinuities in the inner surface of the Waveguide result which induce arcing at higher levels of energy transmission. The effect of these discontinuities is particularly significant in tubes for very high frequency applications (e.g., 30,000 me.) by reason of the short wavelength of the transmitted energy.

It has been mentioned above that in systems involving the use of two or more AT-R tubes difiiculty is frequently experienced in locating the tubes sufliciently close together because of the bulk of the mountings. However, an even greater problem in the use of more than one tube of the known types has been caused by the unavoidable variations between the performance characteristics of tubes of the identical type. For example, the failure of one tube to arc, or to are promptly, on imposition of a burst of high level energy tends to produce distortion in the character of the energy pulse transmitted in the associated waveguide. The difference in characteristics of fresh identical tubes or in the change in characteristics of tubes during use commonly is attributable to even slight differences in the ionizable gas fills. Even though nearly identical gas fills might be realized at the time the tubes are fabricated, variations in reaction rates of the gas fill with the materials of the tubes tend to produce difference in the gas fills during the lives of the tubes.

It is, therefore, an object of this invention to provide a Waveguide transmission control tube capable of being accurately mounted in a wave guide system without auxiliary bulky mounting or clamping devices.

It is a further object to provide a control tube of the above type which is adapted to be mounted in the waveguide system in such manner that objectionable discontinuities in the waveguide are effectively avoided.

A still further object is to provide a control tube having a plurality of resonant cavities and including means for maintaining substantially identical performance characteristics of the cavities during the life of the tube.

In the illustrative embodiment of my invention described in detail below, the foregoing objects are accomplished in a tube of the A-TR type in which the body portion of the tube includes a passage which in effect constitutes a section of the waveguide with which the tube is associated. A plurality of resonant cavities are provided within the tube body, each cavity having a. resonant window at one end thereof flush with the surface of the passage through the tube body. Gas fill reservoirs for each of the resonant cavities are also provided in the tube structure and, as an important feature of the invention, the reservoirs are interconnected by passage means which facilitates free movement of the gas fill back and forth between the reservoirs so that the composition of the gas fills in the various reservoirs and their corresponding resonant cavities are maintained identical during the life of the tube.

Other objects, features and advantages of the devices of this invention will be apparent from the following detailed description and appended drawings in which:

Fig. l is an elevational view, part-1y broken away, of an ATR tube exemplifying an embodiment of the present invention;

Fig. 2 is a transverse cross-sectional view along the line 22 in Fig. l; and

Fig. 3 is a perspective view of the tube of Figs. 1 and 2 showing the manner of mounting the tube in a waveguide system.

The tube illustrated in the drawings includes a main body element consisting of two complementary body portions and 11. The mating faces of the body portions are stepped, as best shown in Fig. 1, so that when the two portions are secured together as by well known soldering or brazing techniques, opposed sections 16, 17 and 18, 19 of the mating faces cooperate to define a continuation within the tube body of the rectangular waveguide 12 with which the tube is to be employed as shown in Fig. 3. After the body portions are secured together the outer end surfaces 13, 14 of the body are carefully machined to provide good contact with the flanges 15 of the waveguide couplers. Openings through the body of the tube are provided to receive the mounting bolts 21 for clamping together the flanges and tube, also as shown in Fig. 3.

In the particular device illustrated herein, two resonant cavities 22 and 23 are provided within the tube body on opposite sides of the waveguide passage through the body. Resonant windows comprising conducting frame portions 24 and irises 25 of dielectric material such as, for example, glass or ceramic are sealed into the openings of the resonant cavities into the waveguide. As

shown in Fig. 2, the windows are of larger cross-section than the main portions of the cavities and are shaped to seat in enlargements of the cavities immediately adjacent the waveguide. It is to be understood of course that this relative size of the Windows and cavities may difier substantially from that shown in Fig. 2. For example, with proper provision for mounting the windows, they may be substantially smaller than the cross-sectional areas of the cavities. The techniques involved in achieving the necessary gas-tight sealing of the irises to the frame portions and the sealing of the frames to the metallic body of the tube are well known and need no elaboration here. However, it is important that the windows be carefully sealed in such position that the outer surfaces thereof (with respect to the resonant cavities) be precisely flush with the surface of the waveguide passage through the tube body. With the particular construction contemplated by my invention, this accurate alignment of windows and waveguide walls, thereby avoiding discontinuities in the waveguide surface conducive to arcing, is relatively simple of accomplishment, since the operation is carried out before the two body portions are secured together, and the critical area is readily available to visual inspection.

It will be apparent that in the employment of the construction described above, the critical adjustment of the window with respect to the inner surface of the waveguide is in effect accomplished under ideal conditions during manufacture of the tube rather than during installation of the tube in an opening in the wall of the waveguide as has been done heretofore. The resultant elimination of discontinuities which previously gave rise to arcing within the waveguide at relatively low values of high level transmission makes possible the use of tubes of this invention in the transmission of microwave energy at higher powers. Where it is desired to take full advantage of this feature of my improved tubes, ceramic rather than glass irises may be employed because of the higher operating temperatures incident to operation at such higher powers. However, because of the inherent porosity of ceramic materials, irises of substantially greater thicknesses than the corresponding glass irises desirably are employed in order to etfect the required gas seal of the resonant cavity. This is accomplished in devices of the present invention by employing ceramic irises of appreciable thickness, corresponding to an integral multiple of an effective half wave-length of the transmitted energy for which the tube is designed. In this way the electrical conditions appear the same at the inner surface of the iris as at the surface of the waveguide. For example, for use at frequencies in the range of 30,000 mc., the thickness of the ceramic iris is desirably an effective single half wave-length in thickness.

As shown in Fig. 2, tuning screws 26 and 27 having lock nuts 28 and 29 are provided for tuning the cavities 22 and 23 to the desired resonant frequency. It will be readily apparent from the drawing that the outer enlarged portions of the tuning screws have threaded surfaces engaging correspondingly threaded surfaces in the openings extending from the back walls of the resonant cavities to the exterior of the main body portion of the tube so that axial movement of the ends of the screws within the resonant cavities is accomplished by rotation of the screw. The inner portions 30 and 31 of the screws are of reduced diameter and are machined to fit accurately the openings 32 and 33 in the back walls of the resonant cavities. Extending axially through the screws are passages 34 and 35 of capillary dimensions. The diameters of these passages are critical only to the extent that the openings of the passages at the cavity ends of the screws must not be so great as to effect the electrical characteristics of the cavities, but must be sufficiently large to permit free movement of the gas fill of the tube into and out of the cavities.

The outer ends of the tuning screws are enclosed by generally cup-shaped elements 36 and 37 which are soldered or brazed to the main body portion of the tube. Circular bosses 38 and 39 are provided on the outside of the main body portion to facilitate positioning and sealing of the open ends of the cup-like elements to the body of the tube. Elements 36 and 37 cooperate with the outer surface of the tube body to define gas-fill reservoirs 40 and 41 which are in communication with their respective resonant cavities through the axial passages through the tuning screws.

In order to insure initial identity of gas fills in the reservoirs and cavities and the maintenance of identical gas fills during the life of the tube, the reservoirs 40 and 41 are connected by a passage 42 which extends through the main body portion of the tube with extremities at the surfaces of the tube enclosed by the cup-shaped elements 36 and 37 as shown in Fig. 1. A portion of the passage is in each of the main body portions of the tube with the inner extremities of the two sections of the passage registering at the mating faces of the body portions when the body portions are properly assembled.

In the assembly of the device described, the windows are first sealed into the body portions of the tube, which in turn are soldered or brazed together in proper relation. The tuning screws are then inserted in the openings provided in the body and adjusted to afford the desired tuning of the resonant cavities. The reservoir chambers are then soldered to the body of the tube preparatory to evacuating and filling the tube with an ionizable gas mixture such as, for example, a mixture of hydrogen, argon, and water vapor in proportions well known in the art.

The tube is evacuated and then filled with the gas mixture by means of copper tubulation 43 soldered or brazed into the reservoir shell 37. After the tube has been filled with gas at the appropriate pressure it is sealed off as shown in Fig. 2 and a small cap 44 is soldered over the sealed end of the tubulation to protect it from damage.

It will be evident that the gas which is supplied to the reservoir 41 will pass not only into the resonant cavity 23, but will also flow freely into reservoir 40 and its associated cavity 22 by virtue of the passage 42 connecting the two reservoirs. Furthermore, during use of the tube, as the gas in one cavity tends to change in composition as, for exmple, by reason of the familiar cleaning up phenomenon, the diffusion of the gas fill throughout the system as described rapidly causes the gas in that cavity to become again identical with the gas in the other cavity of the tube. In this way the lack of identity of performance by reason of differences of gas fills in the various tubes of plural tube systems, which heretofore has been a frequent source of difficulty, is eliminated.

It will also be obvious from the foregoing description of the invention that the resonant cavities and their windows may be arranged at any predetermined desired spacing along the waveguide section of the tube without concern as to any special design of clamping arrangements which might be complicated by a very close spacing of the Windows. For example, in one tube of the type herein disclosed, which is operated at a center band frequency of 34,860 me. and a peak power level or" 100 kw., the centers of the resonant windows are spaced at a distance of only an effective one-half Wave-length apart along the waveguide section of the tube, the dimension in this particular tube being only 0.212 inch.

Although the particular tube described herein includes only two resonant cavities, it will be understood that three or more cavities may be employed. For example, a tube of this type may have four cavities with the cavities arranged in two directly opposed pairs on opposite sides of the waveguide passage through the tube. It Will of course be understood that where more than two cavties are involved, a plurality of passages having the function of passage 42 shown in Fig. 1 will be necessary to interconnect the associated reservoirs.

It will be recognized that the foregoing construction is subject to a latitude of rearrangement and varied application, and consequently it is appropriate that the appended claims be accorded a latitude of interpretation consistent with the spirit and scope of the invention,

What is claimed is:

1. A switching tube of the A-T-R type for controlling transmission of energy in a hollow wave guide system, said tube comprising a block of conducting material having spaced apart parallel end surfaces and having a rectangular passage formed therein, said passage being open at its ends and extending from one to the other of said end surfaces for the transmission of electromagnetic energy therethrough, first and second resonant cavities formed Within said block at spaced apart positions along said passage and proximate opposite broad surfaces of said passage, each of said cavities being filled with an ionizable gas and coupled to said passage by a resonant window structure arranged flush with its corresponding broad surface of said passage, each of said cavities being provided with a tuning screw having an axial passage therethrough adjustably threaded in said block and extending through the wall of the cavity opposite the window structure in a direction normal to the broad surfaces of said passage, and a pair of cup-like members sealed to the outer surface of said block and enclosing the outer ends of said tuning screws and defining with the surface of said block a pair of chambers for containing gas, said block having a passage for gas formed therein extending through a portion not occupied by said rectangular passage and said cavities and interconnecting said chambers.

2. A switching tube of the ATR type for controlling transmission of energy in a hollow rectangular wave guide system, said switching tube comprising a block of generally rectangular cross-section formed of conducting material and having a pair of spaced apart parallel end surfaces adapted to be ab-utted against the flange faces of a pair of correspondingly spaced rectangular wave guide couplers, said block having a passage of rectangular cross-section and dimensions corresponding to the dimensions of the system wave guide formed therein and extending from one to the other of said end surfaces for the transmission of electromagnetic wave energy therethrough, a pair of resonant cavities formed Within said block at spaced apart positions along said passage and proximate opposite broad surfaces of said passage, each of said cavities being filled With ionizable gas and coupled to said passage by a resonant window structure flush with its corresponding broad surface of said passage, said window structures being pervious to electromagnetic energy transmitted through said passage but impervious to the gas within said cavities, each of said cavities being provided with a tuning screw having an axial passage therethrough adjustably threaded in said block and extending through the back wall of the cavity in a direction normal to the broad surfaces of said passage and having its outer end accessible at a surface of said block, and a pair of cup-like elements sealed to said block and enclosing the outer ends of the tuning screws and defining with said block a pair of gas chambers, said block having a passage formed therein extending through a portion of the block not occupied by said passage and said cavities and interconnecting said chambers.

References Cited in the file of this patent UNITED STATES PATENTS 2,444,303 McCarthy June 29, 1948 2,524,268 McCarthy Oct. 3, 1950 2,627,573 Riblet Feb. 3, 1953 2,678,408 Roberts May 11, 1954 2,688,120 Caldwell Aug. 31, 1954 2,697,800 Roberts Dec. 21, 1954 2,710,932 Heins June 14, 1955 

